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Please read: We measured differences in gene expression in two colonies of Varroa-susceptible and two colonies of Varroa-tolerant bees.

Background
The parasitic mite, Varroa destructor, is the most serious pest of the western honey bee, Apis mellifera, and has caused the death of millions of colonies worldwide. This mite reproduces in brood cells and parasitizes immature and adult bees. We investigated whether Varroa infestation induces changes in Apis mellifera gene expression, and whether there are genotypic differences that affect gene expression relevant to the bee's tolerance, as first steps toward unravelling mechanisms of host response and differences in susceptibility to Varroa parasitism.
Results
We explored the transcriptional response to mite parasitism in two genetic stocks of A. mellifera which differ in susceptibility to Varroa, comparing parasitized and non-parasitized full-sister pupae from both stocks. Bee expression profiles were analyzed using microarrays derived from honey bee ESTs whose annotation has recently been enhanced by results from the honey bee genome sequence. We measured differences in gene expression in two colonies of Varroa-susceptible and two colonies of Varroa-tolerant bees. We identified a set of 148 genes with significantly different patterns of expression: 32 varied with the presence of Varroa, 116 varied with bee genotype, and 2 with both. Varroa parasitism caused changes in the expression of genes related to embryonic development, cell metabolism and immunity
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Re: Research on bee diseases, parasites, and diet/nutrition.

The pathways suggested by this study to be associated with honey bee response to Varroa parasitism are schematized hypothetically in Fig. 2. Responses to Varroa can be grouped in two main categories, one related to deformed bee adults occasioned by the presence of the Deformed Wing Virus (DWV) often associated with Varroa parasitism, and a second category of genes that are related to cognitive impairment.

Re: Research on bee diseases, parasites, and diet/nutrition.

BEHAVIOR
Changes in Infestation, Cell Cap Condition, and Reproductive Status of
Varroa destructor (Mesostigmata: Varroidae) in Brood Exposed to
Honey Bees With Varroa Sensitive Hygiene
JEFFREY W. HARRIS,
1
ROBERT G. DANKA, AND JOSE“ D. VILLA
USDAŠARS, Honey Bee Breeding, Genetics and Physiology Laboratory, 1157 Ben Hur Road, Baton Rouge, LA 70820
Ann. Entomol. Soc. Am. 105(3): 512Š518 (2012); DOI: http://dx.doi.org/10.1603/AN11188
ABSTRACT Honey bees (Apis mellifera L.) bred for Varroa sensitive hygiene (VSH) selectively
remove pupae infested with Varroa destructor Anderson & Trueman (Mesostigmata: Varroidae) from
capped brood that is inserted into the nest. After 1 wk, remaining brood cells tend to have been
uncapped and recapped, and remaining mites are mostly infertile. A primary goal of this experiment
was to compare the reproductive status of mites that remained in recapped and normally capped cells
after a 1-wk exposure to VSH and control colonies. Differences in distribution of fertile mites in
normally capped brood cells between VSH bees and control bees may suggest that the stimulus for
hygiene is related to reproduction by mites. IdentiŽcation of stimuli triggering VSH behavior could
be used to develop new bioassays for selective breeding of this important resistance mechanism.
Combs of capped brood that were exposed to control bees had 10 times more pupae with fertile mites
in normally capped brood as did VSH bees (6.7 and 0.7%, respectively). They also had 3 times more
pupae with infertile mites in normally capped brood than did VSH bees (1.4 and 0.5%, respectively).
Thus, VSH bees targeted fertile mites by a 3:1 ratio by either removing or uncapping and recapping
their host pupae. Biased removal of mite-infested pupae with fertile mites suggested that stimuli
triggering VSH behavior were enhanced by the presence of mite offspring within the brood cell. This
bias for fertile mites is not seen during experiments of short 3-h duration. The differing results are
discussed relative to a behavioral threshold model for hygienic behavior in honey bees in which
different experimental protocols may reßect activities of honey bees having different sensitivities to
pupae infested by fertile mites. In addition, mortality of mite offspring was signiŽcantly higher in
recapped cells than in normally capped cells and contributed to decreased reproduction by the mites.
KEY WORDS honey bee, varroa mite, Varroa sensitive hygiene
Infestation by Varroa mites (Varroa destructor Anderson & Trueman [Mesostigmata: Varroidae]) remains
the most signiŽcant health issue to honey bees (Apis
mellifera L.) (Rosenkranz et al. 2010). This parasitic
mite is usually managed with acaricides, but use of
in-hive chemicals leads to chemical residues in honey
and wax (Wallner 1999, Martel et al. 2007), development of genetic-based resistance of mites to chemicals
(Elzen et al. 2000), and synergistic effects between
chemicals that can adversely affect bee health (Johnson et al. 2009). One solution to these problems would
be the development and implementation of honey
bees with genetic-based resistance to Varroa mites.
Several behavioral mechanisms that confer tolerance
or resistance to Varroa mites in honey bees have a
genetic basis, and some of these have been enhanced
through selective breeding (Boecking and Spivak
1999, Rinderer et al. 2010).
Varroa sensitive hygiene (VSH) is a genetic-based
behavioral resistance in which Varroa-infested pupae
are removed from ca